1. Field of Invention
The invention relates to a sheet conveying device, for use in an image forming apparatus, that conveys sheets to a recording unit, by holding the sheets between a feed roller and a pinch roller.
2. Description of Related Art
Printing devices, such as ink jet printers, are provided with sheet conveying devices for conveying sheets mounted on a sheet cassette one by one to a recording or printing unit. The sheet conveying device includes a metal feed roller that is driven by a drive source to rotate, and a plastic pinch roller pressed against the feed roller. The sheet is held between the feed roller and the pinch roller and conveyed to the recording unit.
To increase a printing accuracy of the printing devices, an accuracy of a sheet conveyance with the sheet conveying device needs to be increased. Especially, the ink jet printers that perform printing in high dot density, require the higher sheet conveying accuracy.
To increase an accuracy of a sheet conveying speed, the pinch roller and the feed roller of the sheet conveying device need to be firmly and uniformly pressed against each other to prevent improper sheet feeding. To achieve this, for example, Japanese Laid Open Patent Publication No. 9-142691 discloses a plurality of roller holders that rotatably support the pinch roller at one end thereof and springs that urges the roller holder at rear side ends thereof.
Recently, a margin at an end of the sheet tends to be reduced, so that distance between a printing portion and a nip portion between the feed roller and the pinch roller need to be reduced.
However, reduction of the distance between the printing portion and the nip portion is physically limited. As the distance between the printing portion and the nip portion becomes shorter, the pinch roller needs to be supported to press the feed roller firmly. In the sheet conveying device having the pinch roller and the feed roller pressed firmly against each other, a rear end of the sheet being conveyed flicks or springs due to an impact applied when the rear end of the sheet passes through the nip portion between the pinch roller and the feed roller. This causes improper sheet feeding or variances in sheet feeding amounts, resulting in poor image formation.